Optical information recording medium, method of manufacturing thereof, and method of recording and reproduction

ABSTRACT

An optical information recording medium is provided with a plurality of information layers ( 2, 3 ), each of which has a sector structure in which a data area ( 8, 12 ) is divided in the circumferential direction by a sector address ( 9, 13 ). The positions of the sector addresses ( 9, 13 ) of the respective information layers ( 2, 3 ) coincide in the circumferential direction. This can prevent errors during reproduction caused by the effect of other information layers and stabilize recording characteristics, resulting in an increased recording capacity of a rewritable recording medium having a plurality of information layers with a sector structure.

This application is a continuation of application Ser. No. 09/786,735,filed Mar. 8, 2001, now U.S. Pat. No. 6,795,389 which is a 371 ofPCT/JP99/04828, filed 6 Sep. 1999, which applications are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a recording medium having a multilayerstructure in which optically recordable and reproducible informationlayers are laminated, and to a recording/reproducing method and amanufacturing method for the same.

BACKGROUND ART

Conventionally, optical disks or optical cards are known as opticalinformation recording media on which information can be recorded orreproduced optically. These recording media use a semiconductor laser asa light source, and a great deal of information can be recorded orreproduced by irradiating the recording media with light that is finelyfocused by a lens.

At present, there is much research on the above recording media toimprove their recording capacities. For example, a recording mediumhaving a multilayer structure, where recording capacity is doubled bylaminating information layers for recording or reproducing informationsignals, has been proposed (U.S. Pat. No. 5,726,969). Under suchcircumstances, read-only DVD-ROM disks including two information layershave been put into practical use.

On the other hand, optical disks that can be recorded in the user'senvironment have been achieved using a phase changeable material, amagneto-optical recording material, a dye material, or the like. Thereare two systems for recording signals on such optical disks: asector-structure system and a continuous recording system. The former isused mainly to record data information, while the latter is used torecord sound information, such as CD-Rs.

In the optical disks having a sector structure, an area for managinginformation to be recorded and a data area on which information signalsare recorded by users are separated. However, when the recording systemof a sector structure is applied to a multilayer recording medium,reproduced signals are distorted because of the recorded state ofadjacent layers.

FIG. 9 shows a cross section of a conventional two-layer disk and anexample of reproduced signals from an information layer. In thetwo-layer disk shown in FIG. 9( a), a first information layer 2 and asecond information layer 4 are formed on a substrate 1, and a separatinglayer 3 is provided between the two information layers. On top of that,a protective substrate 5 is formed.

The first information layer 2 has a sector structure including a dataarea 8 for recording information signals and a sector address 9 spacedat predetermined intervals along the length of the data area. The sectoraddress 9 is used for management information for recording/reproducinginformation signals. Similarly, the second information layer 4 alsoincludes a data area 12 and a sector address 13.

In FIG. 9( a), the first information layer 2 is not recorded, whereassignals are recorded on the second information layer 4.

FIG. 9( b) shows reproduced signals from the second information layer 4.In this case, since transmissivity of the first information layer 2 isunchanged, constant signals in accordance with a pattern recorded on thesecond information layer 4 can be reproduced.

On the other hand, in FIG. 9( c), the first information layer 2 isrecorded; FIG. 9( d) shows reproduced signals in such a case. Here, thefirst information layer 2 has the characteristic in which itstransmissivity is increased by recording information. As shown in FIG.9( d), the reproduced signals from the second information layer 4 have awaveform whose amplitude is increased in the area corresponding to therecording area of the first information layer 2.

As described above, in an optical disk having a sector structure,signals are recorded only on the data area, not on the sector address.Therefore, when information signals are reproduced, the amplitude ofreproduced signals and the signal level fluctuate significantlydepending on the recorded state of the opposite layer. In particular,when the reproduced signals from the second information layer aredemodulated, reproduction errors are caused in the area corresponding tothe boundary between the address portion and the data area of the firstinformation layer, so that the recorded information cannot bedemodulated correctly.

Similarly, in recording, the amount of light that reaches the secondinformation layer varies depending on the recorded state of the firstinformation layer, so that information does not recorded correctly.

DISCLOSURE OF INVENTION

The present invention is intended to solve the conventional problemsdescribed above and has an object of providing an optical informationrecording medium that can prevent the effect of the recorded state ofother information layers and can be reproduced stably regardless of thelevel fluctuation of reproduced signals, a method forrecording/reproducing signals on/from the optical information recordingmedium, and a method for manufacturing the same.

In order to achieve the above object, a first optical informationrecording medium of the present invention includes a substrate and atleast two information layers formed on the substrate. The informationlayer is formed of a thin film that shows a change that is opticallydetectable by irradiation of light beams. A separating layer that istransparent to a wavelength of the light beams is formed between theinformation layers. Each information layer has a sector structureincluding a sector address and a data area that are divided in thecircumferential direction. The positions of the sector addresses of therespective information layers coincide in the circumferential direction.The optical information recording medium described above can preventerrors during reproduction caused by the effect of other informationlayers, even in the case of an information recording medium ofmultilayer recording type with a sector structure, and thus stabilizingits recoding characteristics.

The first optical information recording medium includes a firstsubstrate and a second substrate having a sector structure including asector address and a data area that are divided in the circumferentialdirection. A first information layer is formed on the first substrate,and a second information layer opposed to the first information layer isformed on the second substrate. It is preferable that the position ofthe sector address of the first substrate and the position of the sectoraddress of the second substrate coincide in the circumferentialdirection. The optical information recording medium described above canprevent errors during reproduction caused by the effect of otherinformation layers, even in the case of an information recording mediumof multilayer recording type with a sector structure, and thus stabilizeits recording characteristics.

Furthermore, it is preferable that the amount of dislocation between thesector addresses of the respective information layers in thecircumferential direction be smaller than the sum of the length of thegap between the sector address and the data area and the length of aguard data in the data area. The amount of dislocation within the aboverange can ensure the amplitude of reproduced signals of the data signalsin the data area.

It is preferable that each information layer further includes amanagement area, and that a sector position identifier for identifyingthe position of a sector is located in the area other than the dataarea, the sector address, and the management area of each informationlayer so as to have a certain relationship to the sector address of eachinformation layer in the circumferential direction. The opticalinformation recording medium described above can facilitate adjustingthe position of each information layer.

It is preferable that the sector position identifier is arranged inproximity to the management area at the inner circumferential regionthereof, and that the shape of the sector position identifier formed onthe information layer closest to the substrate is different from theshape of the sector position identifier formed on the other informationlayers. The optical information recording medium described abovefacilitates adjusting the position of each information layer furtherbecause the information layer to which the detected sector positionidentifier belongs can be distinguished easily.

It is preferable that each of the first and the second substrate furtherincludes a management area, and that a sector position identifier foridentifying the position of a sector is located in the area other thanthe data area, the sector address, and the management area of each ofthe first and the second substrate so as to have a certain relationshipto the sector address of each of the substrates in the circumferentialdirection. The optical information recording medium described above canfacilitate adjusting the position of each information layer.

It is preferable that the sector position identifier be arranged inproximity to the management area at the inner circumferential regionthereof, and that the shape of the sector position identifier formed onthe first substrate is different from the shape of the sector positionidentifier formed on the second substrate. The optical informationrecording medium described above facilitates adjusting the position ofeach information layer further because the information layer to whichthe detected sector position identifier belongs can be distinguishedeasily.

Next, a second optical information recording medium of the presentinvention includes a substrate and at least two information layersformed on the substrate. The information layer is formed of a thin filmthat shows a change that is optically detectable by irradiation of lightbeams. A separating layer that is transparent to a wavelength of thelight beams is formed between the information layers. A firstinformation layer, which is one of the information layers, has a sectorstructure including a sector address and a data area that are divided inthe circumferential direction. The information layers other than thefirst information layer are provided with spiral guide grooves formed onan entire surface of a data area. The optical information recordingmedium described above does not require adjustment of the position ofthe sector address of each information layer, so that an opticalinformation recording medium, in which the positions of the sectoraddresses of the respective information layers coincide in thecircumferential direction, can be obtained.

In the second optical information recording medium, it is preferablethat a sector address composed of a recording mark formed by irradiationof light beams be provided on the guide grooves of the informationlayers other than the first information layer so as to be at the samecircumferential position as that of the sector address of the firstinformation layer. The optical information recording medium describedabove allows the signals reproduced from the sector address of eachinformation layer to provide equal quality. In addition, the signals ofthe address portion of each information layer can be reproduced with thesame simple circuit.

It is preferable that the second optical information recording mediumincludes a first substrate having guide grooves with a sector structureincluding a sector address and a data area that are divided in thecircumferential direction and a second substrate having spiralcontinuous guide grooves, and that a first information layer is formedon the first substrate and a second information layer opposed to thefirst information layer is formed on the second substrate. The opticalinformation recording medium described above does not require adjustmentof the position of the sector address of each information layer, so thatan optical information recording medium, in which the positions of thesector addresses of the respective information layers coincide in thecircumferential direction, can be obtained.

Furthermore, it is preferable that a sector address composed of arecording mark formed by irradiation of light beams is provided on thesecond information layer so as to be at the same circumferentialposition as that of the sector address of the first substrate. Theoptical information recording medium described above allows the signalsreproduced from the sector address of each information layer to provideequal quality. In addition, the signals of the address portion of eachinformation layer can be reproduced with the same simple circuit.

Next, a third optical information recording medium of the presentinvention includes a substrate and at least two information layersformed on the substrate. The information layer is formed of a thin filmthat shows a change that is optically detectable by irradiation of lightbeams. A separating layer that is transparent to a wavelength of thelight beams is formed between the information layers. Each informationlayer is provided with a data area on guide grooves and a sector addresscomposed of a recording mark formed by irradiation of light beams. Thepositions of the sector addresses of the respective information layerscoincide in the circumferential direction.

Next, a fourth optical information recording medium of the presentinvention includes a substrate and at least two information layersformed on the substrate. The information layer is formed of a thin filmthat shows a change that is optically detectable by irradiation of lightbeams. A separating layer that is transparent to a wavelength of thelight beams is formed between the information layers. Each informationlayer has a sector structure including a sector address and a data areathat are divided in the circumferential direction. A recording mark isformed in the recording areas of all the information layers except theinformation layer most distant from the substrate. The opticalinformation recording medium described above can prevent errors in arecording power suitable for the information layer from occurring.

Next, a first recording/reproducing method for an optical informationrecording medium of the present invention is a method forrecording/reproducing information signals on/from the opticalinformation recording medium using an optical recording/reproducingapparatus. The optical information recording medium includes asubstrate, at least two information layers formed on the substrate, anda separating layer formed between the information layers. Theinformation layer is formed of a thin film that shows a change that isoptically detectable by irradiation of light beams, and the separatinglayer is transparent to a wavelength of the light beams. Signals havinga predetermined pattern are recorded on the recording areas of all theinformation layers except the information layer most distant from thesubstrate when the optical information recording medium is judged to bein the non-recorded state. According to the recording/reproducing methodfor an optical information recording medium described above, therecording of signals having a predetermined pattern can also serve forthe recording to manage faults in an optical recording medium. Thus, themethod is suitable for the recording of data information that requires arelatively small data capacity and a large number of files.

In the first recording/reproducing method for an optical informationrecording medium, it is preferable that the signals having apredetermined pattern are recorded on the information layer closest tothe light beams, and then sequentially recorded on the other informationlayers in the order in which each information layer is positioned withrespect to the light beams.

Next, a second recording/reproducing method for an optical informationrecording medium of the present invention is a method forrecording/reproducing information signals on/from the opticalinformation recording medium using an optical recording/reproducingapparatus. The optical information recording medium includes asubstrate, at least two information layers formed on the substrate, anda separating layer formed between the information layers. Theinformation layer is formed of a thin film that shows a change that isoptically detectable by irradiation of light beams, and the separatinglayer is transparent to a wavelength of the light beams. Informationsignals are recorded on the optical information recording medium in sucha manner that a first information layer, which is closest to the lightbeams, is recorded at the beginning, and then a second information layeris recorded after the entire surface of the recording area of the firstinformation layer has been recorded. According to therecording/reproducing method for an optical information recording mediumdescribed above, the recording of signals having a predetermined patterncan also serve for the recording to manage faults in an opticalrecording medium. Thus, the method is suitable for the recording ofcontinuous signals that require a large capacity for a file, such asvideo signals.

In the second recording/reproducing method for an optical informationrecording medium, it is preferable that the information signals arerecorded on the information layers sequentially in the order in whichthe information layers are positioned with respect to the light beams.

Next, a first method for manufacturing an optical information recordingmedium of the present invention includes: a first film forming step offorming a first information layer on a first substrate; a second filmforming step of forming a second information layer on a secondsubstrate; a sector position adjusting step of placing the firstinformation layer and the second information layer opposed to each otherso that a sector position of the first information layer and a sectorposition of the second information layer coincide, and a bonding step ofbonding the first information layer and the second information layertogether using at least a separating layer. The first substrate hasguide grooves with a sector structure including a sector address and adata area that are divided in the circumferential direction. The firstinformation layer is formed of a thin film that shows a change that isoptically detectable by irradiation of light beams. The second substratehas guide grooves with a sector structure including a sector address anda data area that are divided in the circumferential direction. Thesecond information layer is formed of a thin film that shows a changethat is optically detectable by irradiation of light beams. The abovemanufacturing method can prevent errors during reproduction caused bythe effect of other information layers and provide an informationrecording medium of multilayer recording type with a sector structurethat can stabilize recording characteristics.

In the first method for manufacturing an optical information recordingmedium, it is preferable that the method further includes a hardeningstep, in which the separating layer is made of a ultraviolet curableresin, the first and the second information layer are bonded togethervia the layer of ultraviolet curable resin, a sector position isadjusted in the sector position adjusting step before the ultravioletcurable resin is hardened, and irradiation of ultraviolet rays forhardening the ultraviolet curable resin is performed after theadjustment of the sector position has been completed.

Furthermore, in the first method for manufacturing an opticalinformation recording medium, it is preferable that each of thesubstrates further includes a sector position identifier for identifyingthe position of a sector, and that the sector position identifier islocated in an area other than the data area, the sector address, and amanagement area so as to have a certain relationship to the guidegrooves with a sector structure in the circumferential direction. Theposition of the sector position identifier is detected in the sectorposition adjusting step so that the amount of dislocation between thesectors of the respective information layers is adjusted based on aresult of the detection. The above method can facilitate adjusting theposition of each information layer.

Next, a second method for manufacturing an optical information recordingmedium of the present invention includes: a first film forming step offorming a first information layer on a first substrate; a sectorposition adjusting step of placing a stamper and the first informationlayer opposed to each other so that a sector position of the firstinformation layer and a sector position of the stamper coincide; abonding step of bonding the first information layer and the stampertogether via a separating layer formed of a transparent resin layer andhardening the separating layer; a stripping step of stripping thestamper and the separating layer from the first substrate; a second filmforming step of forming a second information layer on the surface of thereleased separating layer, and a step of protecting an informationlayer, in which a protective layer or a protective plate is bonded onthe most distant information layer from the substrate. The firstsubstrate has guide grooves with a sector structure including a sectoraddress and a data area that are divided in the circumferentialdirection. The first information layer is formed of a thin film thatshows a change that is optically detectable by irradiation of lightbeams. The stamper has guide grooves with a sector structure including asector address and a data area that are divided in the circumferentialdirection. The above method can prevent errors during reproductioncaused by the effect of other information layers and provide aninformation recording medium of multilayer recording type with a sectorstructure that can stabilize recording characteristics. Thus, the methodis suitable for forming three or more information layers.

In the second method for manufacturing an optical information recordingmedium, it is preferable that three or more information layers areformed on a substrate by repeating the sector position adjusting step,the bonding step, the stripping step, and the second film forming step.The above method allows an arbitrary number of information layers to belaminated.

Furthermore, in the second method for manufacturing an opticalinformation recording medium, it is preferable that the first substrateand the stamper further include a sector position identifier foridentifying the position of a sector, and that the sector positionidentifier is located in an area other than the data area, the sectoraddress, and a management area so as to have a certain relationship tothe guide grooves with a sector structure in the circumferentialdirection. The position of the sector position identifier is detected inthe sector position adjusting step so that the amount of dislocationbetween the sectors of the respective information layers is adjustedbased on a result of the detection. The above method can facilitateadjusting the position of each information layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an optical information recordingmedium according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an optical information recordingmedium according to an embodiment of the present invention and awaveform chart of reproduced signals.

FIG. 3 is a schematic view showing a sector of an optical informationrecording medium according to an embodiment of the present invention.

FIG. 4 is a process chart showing a method for manufacturing an opticalinformation recording medium according to an embodiment of the presentinvention.

FIG. 5 is a process chart showing a method for manufacturing an opticalinformation recording medium according to another embodiment of thepresent invention.

FIG. 6 is a schematic view showing an optical information recordingmedium according to another embodiment of the present invention.

FIG. 7 is a schematic view showing a recording apparatus according to anembodiment of the present invention.

FIG. 8 is a schematic view showing an optical information recordingmedium according to another embodiment of the present invention.

FIG. 9 is a schematic view showing an example of a conventional opticalinformation recording medium and a waveform chart of reproduced signals.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be describedwith reference to the accompanying drawings.

Embodiment 1

FIG. 1 shows a configuration of an optical information recording mediumaccording to Embodiment 1 of the present invention. FIG. 1( a) is across-sectional view of the optical information recording medium, inwhich a first information layer 2 and a second information layer 4 areformed on a substrate 1, and a separating layer 3 is provided betweenthe two information layers. On top of that, a protective plate 5 isformed. Information signals are recorded/reproduced with light beams 7that are focused by an object lens 6 from the side of the substrate 1,and the light through the first information layer 2 is used forrecording/reproducing signals on/from the second information layer 4.

As shown in FIG. 1( b), a data area 8 for recording and reproducinginformation signals and a sector address 9 for managing the position ofdata to be recorded are provided on the surface of the first informationlayer 2. The data area 8 includes spiral guide grooves for tracking orsample pits. The sector address 9 includes address pit trains arrangedin a pattern corresponding to address information.

Furthermore, a management area 10 where information about the type ofrecording medium, recording conditions, or the like has been recorded isprovided in the inner circumference of the recording medium. A diskidentifier 11 for identifying the sector position of the firstinformation layer 2 is provided in the area other than the data area 8,the sector address 9, and the management area 10. The disk identifier 11is located so as to have a certain relationship to the sector address 9.In this embodiment, the disk identifier 11 is formed in the innercircumference of the management area 10.

As shown in FIG. 1( c), the second information layer 4 is provided witha data area 12, a sector address 13, a management area 14, and a diskposition identifier 15 that are formed in the same manner as in thefirst information layer.

The position of the disk position identifier 15 varies depending on themethod for identifying the disk position; in this embodiment, it is thesame as that in the first information layer 2.

As is apparent from FIGS. 1( b) and 1(c), the first information layer 2is identical to the second information layer 4 in the arrangement andthe number of sectors. In addition, the positions of the correspondingsectors in the two information layers coincide in the circumferentialdirection. In other words, the two information layers are arranged sothat the sector address 13 of the second information layer 4 isirradiated with the light beams 7 that have passed through the sectoraddress 9 of the first information layer 2.

FIG. 2 shows the waveform of reproduced signals in the case where thesector positions of the two information layers coincide, as shown inFIG. 1. In FIG. 2( a), the first information layer 2 is not recorded andthe second information layer 4 is recorded. In FIG. 2( c), the firstinformation layer 2 is recorded and the second information layer 4 isrecorded.

FIGS. 2( b) and 2(d) show the amplitude of the reproduced signals fromthe second information layer 4 and correspond to FIGS. 2( a) and 2(c),respectively When the first information layer 2 is not recorded, thereproduced signals are the same as the conventional signals, as shown inFIG 2(b). On the other hand, when the first information layer 2 isrecorded, the amplitude of the reproduced signals is increased becauseof the recorded state of the first information layer 2, as shown in FIG.2( d). However, since the positions of the sector addresses 9, 13 of therespective information layers 2, 4 coincide, the amplitude level of thesignals in the data information area is unchanged. As a result,information signals recoded on the second information layer 4 can bedemodulated stably.

In order to deal with an increase in the level difference between theaddress portion and the data portion, the format for a sector structureincludes a gap area to be arranged between the data area and the sectoraddress. The gap area where no information is recorded is composed of atleast several bits and can compensate for the change in the signal levelcaused by the recorded state of the first information layer.

Since the form of reproduced signals in the sector address isfundamentally different from that in the data area, a slice level is setindividually to the sector address and the data area duringdemodulation. Thus, such an increase in the level difference between thedata portion and the address sector portion does not cause errors duringdemodulation.

As described above, this embodiment allows information recorded on thesecond information layer 4 to be reproduced stably regardless of therecorded state of the first information layer 2. Furthermore, thisembodiment can also function stably with respect to the effect of thelevel fluctuation caused by the light reflected from the recorded secondinformation layer 4.

The foregoing described an example of two information layers. However,the same effect can be obtained by a recording medium having three ormore information layers, in which the sector positions of the respectiveinformation layers coincide.

Next, the amount of allowance of dislocation of the sectors between theinformation layers will be described with reference to the schematicview of a sector as shown in FIG. 3. FIG. 2 shows an example of twoinformation layers between which there is no dislocation. However, thedislocation occurs to some extent in manufacturing a recording medium.In FIGS. 1 and 2, a sector includes two areas: a sector address and adata area. However, gap areas 33, 34 are provided between a data area 31and a sector address 30 to compensate for timing errors of recordingcaused by rotational fluctuation or the like.

Furthermore, the data area 31 for recording data includes data signals32 to be reproduced and guard signals 35, 36 that are recorded beforeand after the data signals 32. The guard signals are used to protect theinformation layer against degradation because of repetitive recording.Therefore, the amplitude of the reproduced signals in the range of thedata signals 32 should be ensured to reproduce the recorded datasignals.

Thus, it is preferable that the amount of dislocation between the twoinformation layers, which has no effect on the range of the data signals32, is not more than the sum of the length of the gap area 33 and thatof the guard data area 35, or is not more than the sum of the length ofthe gap area 34 and that of the guard data area 36.

The foregoing described an example of two information layers. However,the same effect can be obtained by a recording medium having three ormore information layers, in which the sector positions of the respectiveinformation layers coincide with the same precision.

Next, a method for manufacturing an optical information recording mediumof this embodiment will be described. FIG. 4 shows the process for afirst manufacturing method in which the sector positions coincide. FIG.4( a) shows a first film forming step of forming the first informationlayer 2 on a first substrate 1 provided with guide grooves having asector structure. FIG. 4( b) shows a second film forming step of formingthe second information layer 4 on a second substrate 41. The secondsubstrate 41 is provided with the same guide grooves as those in thefirst substrate 1 and acts as a protective plate.

A disk position identifier 42 is provided on the surface of the firstsubstrate 1. The disk position identifier 42 is located in the areaother than the data recording area, the sector address, and themanagement area so as to have a certain relationship to the sector.Similarly, a disk position identifier 43 is provided on the surface ofthe second substrate 41. These disk position identifiers 42, 43 areformed of guide grooves or pit trains.

FIG 4(c) shows a coating step of coating the surface of the secondinformation layer 4 with an adhesive 44, which results in an adhesionlayer. In this process, an ultraviolet curable resin is used as theadhesive 44. FIG 4(d) shows a bonding step of bonding the firstinformation layer 2 on the first substrate 1 and the second informationlayer 4 on the second substrate 41 together via the adhesive 44. Thesubstrates are rotated or pressurized so that the thickness of theadhesive 44 between the substrates 1 and 41 is uniform, if necessary.

FIG. 4( e) shows a position detecting step of detecting the positions ofthe disk position identifier 42 of the first information layer 2 and thedisk position identifier 43 of the second information layer 4 with aphotodetector 45 such as a video camera or the like before the adhesive44 between the information layers 2 and 4 is hardened. Thus, the amountof dislocation between the two disk position identifiers 42 and 43 isdetermined.

In order to facilitate distinguishing the information layer to which thedetected disk position identifier belongs, it is preferable that each ofthe identifiers of the information layers has different shape or size.

FIG. 4( f) shows a position correcting step of fixing one of thesubstrates 1, 41 and rotating the other with a rotating unit 46 so thatthe two disk position identifiers are located to have a certainrelationship to each other, i.e., the sector positions of the twoinformation layers coincide. The positional adjustment, such as rotationof the substrate, is completed when the relationship between the twoidentifiers satisfies certain conditions.

FIG. 4( g) shows a hardening step of hardening the adhesive 44 byirradiation of light of an ultraviolet lamp from the side of the firstsubstrate 1. The process described above can provide a two-layerrecording medium in which the sector positions of the two informationlayers coincide in the circumferential direction.

The disk position identifiers 42, 43 are used for judging thedislocation between the information layers. However, these disk positionidentifiers can be omitted. In that case, a multilayer disk, in whichthe sector positions coincide in the circumferential direction, can beobtained in such a manner that the circumferential position is detectedwith a video camera or the like based on the sector address arrangementin the respective information layers, and then the amount of dislocationis calculated, so that the positions of the two information layers arecorrected by the same process as described above.

In FIG. 4, one video camera is used. However, a plurality of videocameras or CCD sensors can be arranged in the circumferential directionof a disk, which increases the positioning speed and accuracy.

The foregoing described the method for adjusting the dislocation only inthe circumferential direction. However, it is also effective that thedislocation in the radial direction be corrected after the dislocationin the circumferential direction has been corrected. In other words,first, the amount of dislocation in the circumferential direction iscorrected in the step shown in FIG. 4( f). Similarly, the amount ofdislocation in the radial direction is determined with a video camera 45and corrected by moving one of the substrates radially with a diskposition adjusting unit 46. This method allows the sector positions in aplurality of the information layers to coincide both circumferentiallyand radially, so that the effect of dislocation between the informationlayers is reduced further.

In a recording medium used for two-layer recording, information signalsare reproduced by irradiating the two information layers 2, 4 with lightand detecting the change in the reflected light. Therefore, the lightbeams 7 for irradiation must be focused precisely on the informationlayer from which signals are reproduced. In particular, the firstinformation layer 2 is required to have a certain transmissivity withrespect to a wavelength of the light beams 7 so that the light having apredetermined intensity reaches the second information layer 4. In viewof the stability of reproduction of signals from the two informationlayers, it is preferable that the transmissivity of the firstinformation layer be in the range of 30 to 80%.

Furthermore, information is recorded on the second information layer 4in such a manner that the temperature of the portion irradiated with thelight beams 7 at high intensity is raised to change the opticalcharacteristics thereof. Thus, it is necessary that the secondinformation layer satisfies high absorptivity with respect to awavelength of the light beams 7 as well as a large optical change, i.e.,signals in the recorded state are reproduced at high efficiency.

It is preferable that the substrate 1 has a lower optical absorptionwith respect to a wavelength of the light beams 7 for irradiation, andthat concave-convex portions (pits) are formed stably on the surfacethereof. Therefore, a resin material such as polycarbonate, polymethylmethacrylate (PMMA), glass material, or the like is used as a substratematerial.

The second substrate 41 that acts as a protective plate is notnecessarily transparent to the light beams 7. However, it is preferablethat the second substrate 41 be formed of the same material as for thefirst substrate 1 to prevent warping or the like and stabilize itsshape.

The second information layer 4 is formed of a recordable andreproducible thin film, whose optical characteristics are changed byabsorbing the focused light and the change in the thin film can bedetected by the light beams 7. The thin film used for a recording layerthat satisfies these requirements includes the following: a phasechangeable material in which reflectance is changed as the state of athin film is changed by irradiation of light, an organic material, suchas dyes or the like, in which spectral reflectance is changed, and aphotochromic material. Also, some thin films are changed in its shape.

Examples of a phase changeable material include a compound representedby GeSbTe that changes between the amorphous and the crystalline phase,such as a compound based on SbTe, InTe, GeTeSn, SbSe, TeSeSb, SnTeSe,InSe, TeGeSnO, TeGeSnAu, TeGeSnSb, InSbTe, AgInSbTe or the like, anoxide material based on Te—TeO₂, Te—TeO₂—Au, Te—TeO₂—Pd or the like, ora metallic compound that changes between the crystalline and thecrystalline phase, such as a metallic compound based on AgZn, InSb orthe like.

Examples of an organic dye material include a leuco dye based ontriphenylmethane or the like. Examples of a photochromic materialinclude a material based on spiropyran, fulgide, azo or the like.

Recordable information layers are classified into two types according totheir functions: write-once type and rewritable type. The former can berecorded only once and the latter allows the recorded information to berewritten. For the write-once type, only a layer made of a phasechangeable material or an organic dye material is formed on a substrateas an information layer. Alternatively, a two-layer structure includinga thin film layer for absorbing light and a metal layer can be used toform an alloy by irradiation of light.

It is preferable that the information layer includes a plurality oflayers (at least two layers), so that the materials constituting theinformation layer change reversibly and the optical change in therecorded signals is increased. For example, the two-layer structure maybe composed of the following: a dielectric layer and a recording layer,a recording layer and a reflective layer, or a reflective layer and arecording layer. In each structure, the layers are laminated in thisorder from the light incident side. Furthermore, a three-layer structuremay be composed of the following: a dielectric layer, a recording layer,and a dielectric layer or a dielectric layer, a recording layer, and areflective layer. In each structure, the layers are laminated in thisorder from the substrate side. In a four-layer structure, e.g., adielectric layer, a recording layer, a dielectric layer, and areflective layer may be laminated in this order from the substrate side.There is a five-layer structure in which a first reflective layer, adielectric layer, a recording layer, a dielectric layer, and a secondreflective layer may be laminated. As described above, the recordinglayer of a thin film and the dielectric layer are formed in contact witheach other, so that the degradation of a thin film during repetitiverecording can be prevented and the optical change in informationrecording can be increased.

In order to ensure a sufficient amount of light on the secondinformation layer 4, it is preferable that the separating layer (theadhesive 44) is formed of a material having a lower optical absorptionwith respect to the wavelength range of the incident light beams 7, inparticular, the light through the first information layer 2. Therefore,the separating layer may be formed of a transparent adhesive or, likethe substrate, a glass material, a resin material, or the like. When thesubstrates 1, 41 are formed of a resin material, it is preferable thatthe same type of resin material is used for the separating layer toprovide mechanical reliability after bonding. It is more preferable touse an ultraviolet curable resin because the time required for bondingcan be shortened.

The foregoing described the first manufacturing method, in which twoinformation layers are bonded together with a separating layer. Next, asecond manufacturing method, in which the guide grooves of a secondinformation layer are formed by a 2P method, will be described withreference to FIG. 5.

FIG. 5( a) shows a film forming step of forming a first informationlayer 2 on a first substrate 1 provided with guide grooves having asector structure. A disk position identifier 52 is provided on thesurface of the first substrate 1. The disk position identifier 52 islocated in the area other than a data recording area, a sector address,and a management area so as to have a certain relationship to thesector. FIG. 5( b) shows a coating step of coating the surface of astamper 51 provided with guide grooves having a sector structure with atransparent resin layer 54, which results in a separating layer. As withthe first substrate 1, a disk position identifier 53 is provided on thesurface of the stamper 51. It is preferable that the disk positionidentifier 53 of the stamper 51 be different from the disk positionidentifier 52 of the substrate 1 in shape or size so as to facilitatedistinguishing the layer to which the identifier belongs when the diskposition is detected.

FIG. 5( c) shows a bonding step of bonding the substrate 1, on which thefirst information layer 2 opposed to the stamper 51 is formed, and thestamper 51 together via the transparent resin layer 54. At this time,the transparent resin layer 54 is diffused by pressure or rotation so asto be uniform between the substrate 1 and the stamper 51.

FIG. 5( d) shows a position detecting step of detecting the positions ofthe disk position identifier 52 of the first information layer 2 and thedisk position identifier 53 of the stamper 51 with a photodetector suchas a video camera 55 or the like before the transparent resin layer 54between the information layers is hardened. Thus, the amount ofdislocation between the two identifiers is determined.

FIG. 5( e) shows a position correcting step of fixing one of thesubstrate 1 and the stamper 51 and rotating the other with a diskposition adjusting unit 56 so that the two identifiers 52, 53 arelocated to have a certain relationship to each other, i.e., the sectorpositions of the two information layers coincide. The positionaladjustment of the substrate is completed when the relationship betweenthe two identifiers 52 and 53 satisfies certain conditions.

FIG. 5( f) shows a hardening step of hardening the transparent resinlayer 54 by irradiation of light of an ultraviolet lamp from the side ofthe substrate 1. FIG. 5( g) shows a stripping step of stripping thesubstrate 1 at the boundary between the stamper 51 and the transparentresin layer 54.

FIG. 5( h) shows a second film forming step of forming a secondinformation layer 4 on the separating layer formed of the transparentresin layer 54. FIG. 5( i) shows a second coating step of coating thesurface of the second information layer 4 with a protective layer 57,and thus a two-layer disk can be provided.

The use of this method allows many more information layers to belaminated. Specifically, after the steps shown in FIG. 5( a) to 5(h),the surface of a stamper provided with an address format correspondingto a third layer is coated again with an ultraviolet curable resin inthe step shown in FIG. 5( b).

A disk position identifier of the stamper corresponding to the thirdinformation layer may be different from that of the first substrate 1 atleast in shape. Alternatively, it may be the same as that of the stampercorresponding to the second information layer.

Next, in the step shown in FIG. 5( c), the stamper is bonded to thesubstrate on which two information layers have been formed, and thensubjected to the steps shown in FIG. 5( d) to 5(h), resulting in athree-layer disk.

When a plurality of information layers are laminated further, the stepsshown in FIG. 5( b) to 5(h) are repeated, and thus any number ofinformation layers can be laminated.

The disk position identifiers 52, 53 are used for judging thedislocation between the information layers. However, these disk positionidentifiers can be omitted. In that case, a multilayer disk, in whichthe sector positions coincide in the circumferential direction, can beobtained in such a manner that the circumferential position is detectedwith a video camera or the like based on the sector address arrangementin the respective information layers, and then the amount of dislocationis calculated, so that the positions of the two information layers arecorrected by the same process as described above.

In FIG. 5, one video camera is used. However, a plurality of videocameras or CCD sensors can be arranged in the circumferential directionof a disk, which increases the positioning accuracy.

The foregoing described the method for adjusting the dislocation in thecircumferential direction. However, it is also effective that thedislocation in the radial direction be corrected after the dislocationin the circumferential direction has been corrected. In other words,first, the amount of dislocation in the circumferential direction iscorrected in the step shown in FIG. 5( e). Similarly, the amount ofdislocation in the radial direction is determined with the video camera55 and corrected with the disk position adjusting unit 56. This methodallows the sector positions in a plurality of information layers tocoincide both circumferentially and radially, so that the effect ofdislocation between the information layers is reduced further.

Embodiment 2

Embodiment 2 relates to a second method, in which the sector positionsin a plurality of information layers coincide, and to a method forrecording a sector address after a recording medium has been formed.

In this embodiment, the overall configuration of an optical recordingmedium is the same as that shown in FIG. 1( a). FIG. 6( a) shows thestructure of a first information layer 2 on which guide grooves forrecording data and a sector address composed of pit trains are formed.FIG. 6( b) shows the structure of a second information layer 4, on theentire surface of which spiral guide grooves 61 (illustrated partly)equal to a data area 8 of the first information layer 2 are formed.

Furthermore, when a recording medium having a plurality of informationlayers is provided, the same layers as the second information layershown in FIG. 6( b) are formed sequentially, so that any number ofinformation layers can be obtained.

Next, a method for forming a sector address on the second informationlayer 4 will be described with reference to FIG. 7. A multilayerrecording medium 70 having the information layers shown in FIG. 6 isrotated by a disk motor 71 so that signals are reproduced by an opticalpickup 72. The reproduction of signals is performed in such a mannerthat a semiconductor laser 74 in the optical pickup 72 is modulated by alaser driving circuit 73 so as to emit light beams from the opticalpickup 72, with which the optical disk 70 is irradiated.

The light beams reflected by the optical recording medium 70 enter theoptical pickup 72 again. The incident light beams are convertedphotoelectrically by a photodetector 75 and amplified by a preamplifier76 in a reproduction circuit so as to be sent to a control system 77 anda signal reproduction system 78. The control system 77 controls theposition of light beams; the signal reproduction system 78 demodulatessignals. The light beams are focused on the information layer by a focuscontrol circuit 79 in the control system 77, and the focused light beamsare moved to the intended information layer by a focus jump circuit 80.

Next, tracking of the guide tracks on the information layer is performedby a tracking control circuit 81, and the intended track can be scannedby a tracking jump circuit 82.

In the signal reproduction system 78, information signals are providedby demodulating the output of the preamplifier 76 with a demodulationcircuit 83. The information signals thus demodulated are sent to asystem control section 84, where the information signals are convertedinto data information, and are then output to an external controldevice. An address demodulation circuit 85 demodulates the address ofthe track for reproduction. A layer identification circuit 86 identifiesinformation about layers recorded on a management area of the opticalrecording medium and specifies the information layer that is beingreproduced.

Using an apparatus having the above-described configuration, first, thefirst information layer 2 in the multilayer optical recording medium 70,including a sector address is irradiated with light beams. Then, addresssignals formed on the first information layer 2 are reproduced, so thatthe position of the sector address of the first information layer 2 isspecified by the reproduced signals.

In this case, the position of the sector address is based on therelative time interval between address gate signals and rotationsynchronizing signals. The address gate signals indicate a period oftime required for demodulation by the address demodulation circuit 85,while the rotation synchronizing signals are detected by a rotationsynchronous circuit 87 based on the output pulses from the disk motor71. Those pulses correspond to the position of rotation. A dislocationdetector 88 calculates an address delay time d, by which sector addresssignals are delayed with respect to reference pulses that are suppliedonce for every rotation by the rotation synchronous circuit 87.

Next, the focus jump circuit 80 scans the guide grooves 61 on the secondinformation layer 4, and an address gate generator 89 generates addressgate signals in such timing that the address gate signals are delayed bythe address delay time d with respect to the reference pulses from therotation synchronous circuit 87.

A format circuit 90 supplies address information at the timingcorresponding to the address gate signals, and the laser driving circuit73 modulates the output power of the semiconductor laser 74. Thus, theaddress signals are recorded on the second information layer 4 in themultilayer optical recording medium 70.

The above method allows the positions of the sector addresses of thefirst information layer 2 and the second information layer 4 tocoincide. Therefore, the amplitude fluctuation of data signals of thesecond information layer 4 can be suppressed according to the signalsrecorded on the first information layer 2. Furthermore, the process foradjusting the address positions of the two information layers, which iscarried out in Embodiment 1, can be omitted.

There are two types in the above optical recording medium depending onwhen a sector address is formed. In a first type, address information isrecorded during manufacturing. An optical recording medium of this typeincludes information layers, each of which is provided with addressinformation at the time of shipment. Thus, users can record/reproducesignals on the optical recording medium immediately after they haveinstalled it in a recording/reproducing apparatus.

In a second type, a completed optical recording medium includesinformation layers on which only guide grooves without a sector addressare formed. In this type, users have to record address information onthose information layers, which have no sector address. However, since aprocess for recording address information during manufacturing can beomitted, the production cost of an optical recording medium can bereduced.

The foregoing described an example of two information layers. However,multi-layered information layers can be obtained by forming newinformation layers on the second information layer; the new informationlayers have the same structure as the second information layer, in whichguide grooves without a sector address are provided.

Furthermore, the foregoing described the first information layer onwhich a sector address has been formed previously. However, as shown inFIG. 8, both the first information layer (FIG. 8( a)) and the secondinformation layer (FIG. 8( b)) may be formed of the guide grooves 95, 97(illustrated partly) without a sector address, respectively.

In this case, the recording apparatus shown in FIG. 7 can be applied tothe two layers. Specifically, the address gate generator 89 is drivenwith the same timing as the rotation synchronous circuit so that anaddress is recorded on the two information layers at this timing. Thiscan provide an optical recording medium, in which the positions ofaddress signals of the respective information layers coincide.

For an optical recording medium including multi-layered informationlayers, every information layer is formed of guide grooves without asector address. Recording address signals sequentially on the opticalrecording medium thus obtained with the recording/reproducing apparatusshown in FIG. 7 can provide a multilayer optical recording medium, inwhich the positions of address signals of the respective informationlayers coincide.

As described above, an optical recording medium having informationlayers, on each of which address information is recorded with laserlight, allows the signals reproduced from the sector address of eachinformation layer to provide equal quality. In addition, the signals ofthe address portion of each information layer can be reproduced with thesame simple circuit.

As a method for recording a sector address on every information layer,like the above optical recording medium, there are two types dependingon when the sector address is formed. In a first type, addressinformation is recorded during manufacturing. An optical recordingmedium of this type includes information layers, each of which isprovided with address information at the time of shipment. Thus, userscan record/reproduce signals on the optical recording medium immediatelyafter they have installed it in a recording/reproducing apparatus.

In a second type, a completed optical recording medium includesinformation layers on which only guide grooves without a sector addressare formed. In this type, users have to record address information onthose information layers, which have no sector address. However, since aprocess for recording address information during manufacturing can beomitted, the production cost of an optical recording medium can bereduced. In this case, the length of a sector, an address code, or thelike can be set arbitrarily in accordance with the type of informationto be recorded by users and the required capacity.

Embodiment 3

Each of the above embodiments relates to a method for suppressingamplitude fluctuation during reproduction. This embodiment achievesstable recording and reproduction, including signal recording, byfurther reducing the effect of fluctuation factors among informationlayers.

As shown in FIG. 9, in a conventional optical recording medium, thelevel of signals reproduced from a second information layer variesdepending on whether a first information layer is recorded or notrecorded. On the other hand, as shown in FIG. 2, the present inventioncan suppress the amplitude fluctuation in a sector.

However, when light beams are focused on the second information layer,the light beams through the first information layer depend mainly on thethickness of a separating layer and the NA of an object lens. In thecase where the NA of an object lens is 0.5 to 0.6 and the thickness of aseparating layer is 20 to 100 μm, the amount of light that reaches thesecond information layer is affected by the area in the vicinity of alight-focused portion, ranging from about 20 to 100 μm in diameter. Inother words, the amount of light that reaches the second informationlayer varies depending on the recorded state of the first informationlayer in this area. Therefore, errors are caused in a recording powersuitable for the second information layer, when viewed from the pickupside.

On the other hand, in this embodiment, the second and the followinginformation layers are recorded after the entire surface of the firstinformation layer has been recorded during the manufacturing orrecording of a recording medium.

First, the recording of information layers during manufacturing arecording medium will be described. In a recording medium formed by themethod that has been described in Embodiments 1 and 2, signals having apredetermined pattern are recorded on the entire data area of the firstinformation layer. Examples of such signals include those having apattern of modulation that is the same as data information, a pattern ofa specified single period, or a pattern of repetition of specifiedsignals. There is no particular limitation to the pattern of signals, aslong as the average transmissivity of the first information layer in theabove area ranging from 20 to 100 μm in diameter is equal to thetransmissivity of the first information layer when data information isrecorded on the entire area thereof.

Furthermore, there is a method in which the recording of a predeterminedpattern also serves for the recording to manage faults in an opticalrecording medium. In other words, a predetermined recording pattern isused as an information pattern including a code for correcting errors.Information in accordance with this pattern is recorded on the user'sarea in an optical recording medium. Then, a defective sector can beidentified by detecting demodulation errors during reproduction. Inaddition, the fault-management includes allocating an area to besubstituted for the defective sector.

The alternate sector may be provided in the inner or outer circumferenceof the data area or in the last region of each zone, depending on theformat of an optical recording medium. In this embodiment, besides theoperation of fault-management, signals are recorded on an area to besubstituted for the area where recording is inadequate. Furthermore,when a test recording area or the like is provided in the inner or outercircumference of the information layer other than the user's area,signals are also recorded on that area. For a two-layer optical disk,the entire surface of the first information layer is recorded. However,the same effect can be obtained by a multilayer recording medium inwhich all the information layers except at least the most distantinformation layer from light beams are recorded.

When the above process is performed during manufacturing a recordingmedium, signals can be recorded on any position of any information layerat the time of installation of a recording medium of the presentinvention in an optical disk apparatus.

On the other hand, the user's area is not recorded during manufacturing,which reduces the production cost of a recording medium. Instead, theuser's area can be recorded by an optical disk apparatus.

There are two methods for this. The first method is such that the entiresurface of the first information layer is recorded when a recordingmedium is first installed in an optical disk apparatus. This method canprovide the same effect as that described above. Though the initialrecording may cause a loss of time, it can be reduced in the subsequentoperations.

The second method is such that the order of information recording on arecording medium is determined. In other words, the recording isperformed sequentially from the first track of the first informationlayer, and then the second information layer is recorded after theentire surface of the first information layer has been recordedcompletely.

In this case, it is necessary that signals be recorded completely on theentire recording area, including an alternate sector, a test area, orthe like when the recording of the entire surface of the user's area iscompleted. These areas may be recorded in installation of a recordingmedium in an optical disk apparatus, in completion of the predeterminedrecording, or in completion of the recording of the user's area of thefirst information layer.

Furthermore, when the information layer to be recorded is the mostdistant information layer, i.e., in the case of a two-layer disk, it isa second information layer, signals can be recorded on any position ofthe second information layer.

The first and the second method described above may be selected inaccordance with the type of data to be recorded by users. The firstmethod is used for the recording of data information that requires arelatively small data capacity and a large number of files. The secondmethod is suitable for the recording of continuous signals that requirea large capacity for a file, such as video signals.

Each of the above embodiments allows a sectored optical recording mediumhaving a plurality of information layers to be recorded and reproducedstably.

The above embodiments have been described individually. However, it isobvious that a combination of the processes of the respectiveembodiments can provide more stable recording/reproducing operations.

INDUSTRIAL APPLICABILITY

As described above, the present invention can prevent errors duringreproduction caused by the effect of other information layers andstabilize recording characteristics in such a manner that the sectorpositions in a plurality of information layers coincide. In addition,those information layers are recorded sequentially from the informationlayer on the laser beam incident side, allowing for more stablerecording/reproducing operations.

Thus, the present invention can be applied to a rewritable recordingmedium having a plurality of information layers with a sector structureand can increase the recording capacity of a recordable optical disk.

1. A recording/reproducing method for an optical information recordingmedium comprising: recording/reproducing information signals on/from theoptical information recording medium using an opticalrecording/reproducing apparatus, the optical information recordingmedium comprising a substrate, at least two information layers formed onthe substrate, and a separating layer formed between the informationlayers, the information layers formed of a thin film that shows a changethat can be detected optically by light beam irradiation, and theseparating layer being transparent to a wavelength of the light beams,wherein signals having a predetermined pattern are recorded on recordingareas of all the information layers except the most distant informationlayer from the substrate when the optical information recording mediumis judged to be in a non-recorded state.
 2. The recording/reproducingmethod for an optical information recording medium according to claim 1,wherein the signals having a predetermined pattern are recorded on theinformation layer closest to the light beams, and then sequentiallyrecorded on the other information layers in an order in which the otherinformation layers are positioned with respect to the light beams.
 3. Arecording/reproducing method for an optical information recording mediumcomprising: recording/reproducing information signals on/from theoptical information recording medium using an opticalrecording/reproducing apparatus, the optical information recordingmedium comprising a substrate, at least two information layers formed onthe substrate, and a separating layer formed between the informationlayers, the information layer formed of a thin film that shows a changethat can be detected optically by light beam irradiation, and theseparating layer being transparent to a wavelength of the light beams,wherein information signals are recorded on the optical informationrecording medium in such a manner that a first information layer, whichis closest to the light beams, is recorded at the beginning, and then asecond information layer is recorded after an entire surface of arecording area of the first information layer has been recorded.
 4. Therecording/reproducing method for an optical information recording mediumaccording to claim 3, wherein the information signals are recorded onthe information layers sequentially in an order in which the informationlayers are positioned with respect to the light beams.